1. Field of the Invention
This invention relates to a novel reaction cuvette structure and, more particularly, to a novel reaction tray comprised of a plurality of reaction cuvettes for use in automated analysis systems.
2. Description of the Prior Art
In the field of automated analysis, wherein aqueous samples are reacted in turn in respect of one or more analytes, contamination between successive samples in a major problem. In continuous-flow analytical systems as described in Skeggs et al U.S. Pat. No. 3,241,432, issued on Mar. 22, 1966, and in the Smythe et al U.S. Pat. No. 3,479,141, issued on Nov. 18, 1969, both assigned to a common assignee, sample segments are successively introduced into the system by means of a single aspirating probe, In the Skeggs et al patent, a sequence of air-wash liquid-air segments is aspirated between successive sample segments to substantially reduce contamination therebetween. The sample segments, thus separated, are passed as a continuous stream through the analytical system, so as to be reacted and analyzed in "on-line" fashion. During aspiration of each wash liquid segment, the probe is immersed into the wash liquid reservoir to remove contaminants from or "wash" both interior and exterior probe surfaces. In the latter Smythe et al patent, contamination between successive sample segments in the continuous stream is very substantially reduced by introducing an immiscible liquid, e.g., silicone, fluorocarbon oil, etc., between successive sample segments. The immiscible liquid preferentially wets the interior surfaces of the analytical system, to the complete exclusion of the aqueous sample segments. The sample segments are, in effect, completely encapsulated by the immiscible liquid, whereby contamination between successive sample segments is completely avoided.
Also, in analytical systems which do not utilize continuous-flow techniques, hereafter designated discrete systems, a controlled volume of the aqueous sample and appropriate reagents are precisely metered into a reaction cuvette, the depth of color of the reaction mixture being measured to determine the analyte concentration. Generally, such metering is effected by precisely aspirating a predetermined volume of sample or reagent and dispensing the same into the reaction cuvette. Contaminants and other residues from a previous metering operation are removed from the external probe surface by immersing the probe into a wash-liquid reservoir. Often, the probe is reverse-flushed with an appropriate liquid to clean the interior probe surfaces.
In the A. Reichler et al U.S. Pat. No. 4,121,466, issued on Oct. 24, 1978, and assigned to the common assignee, an improved metering or dispensing system, useful in both continuous-flow and discrete systems, is described, wherein contamination between successively aspirated liquids is completely avoided. In such system, the external and internal probe surfaces which normally contact the aqueous liquids, whether sample or reagent, are continuously coated with a thin film of liquid, which is immiscible with such liquids and preferentially wets such surfaces. Also, the aqueous liquid segments aspirated into the probe for dispensing are completely encapsulated within the immiscible liquid. Hence, the interior and exterior probe surfaces are not in contact with the aqueous liquid during either the aspiration or dispense cycles.
Admittedly, the metering system as described in the aforementioned U.S. Pat. No. 4,121,466 provides very beneficial results in positively eliminating contamination between successively dispensed liquid segments and, also, between sources of different liquids into which the probe is selectively immersed. However, when used as a dispenser in a discrete system, the liquid segments, whether sample or reagent, dispensed into the reaction cuvette may be encapsulated within a film of the immiscible liquid. In certain instances, for example, where a surfactant is present in the liquid being metered, there is a strong tendency for the sample or a portion thereof to remain encapsulated within the immiscible liquid film, which is not easily ruptured during the dispensing cycle. Unless such encapsulating film is ruptured, the dispensed liquid segment is not available for reaction. The present invention is particularly directed to a novel reaction cuvette structure for overcoming such shortcomings of the prior art and positively insuring against the formation of such encapsulating film during the dispensing cycle.